A lighting apparatus for lighting a high-intensity discharge lamp used as a headlight of a vehicle has been proposed, for example, in JP-A-2003-318042. In this type of lighting apparatus, a battery voltage is stepped up by a transformer, for example, a direct-current to direct-current (DC-DC) converter. A direct-current to alternating-current (DC-AC) inverter configured as a H-bridge (i.e., full bridge) circuit changes the stepped-up voltage, which is a direct voltage, to an alternating voltage. Thus, the discharge lamp is lit by the alternating voltage.
The lighting apparatus includes a metal casing and a busbar casing having a busbar and a terminal. A printed circuit board having a pad is housed in the metal casing. Circuit components including the DC-DC converter are housed in the busbar casing. The busbar casing is mounted on the metal casing and the terminal of the busbar casing is connected to the pad of the printed circuit board housed in the metal casing. Thus, the circuit components housed in the busbar casing are electrically connected to printed wiring provided on the printed circuit board.
The temperature of the DC-DC converter increases when the DC-DC converter steps up the battery voltage. The DC-DC converter is arranged away from circuit components having a low heat resistance so that heat produced by the DC-DC converter can be prevented from being transferred to the circuit components.
Recently, there has been an attempt to reduce the size of the lighting apparatus for the discharge lamp. However it is difficult to reduce the size of the busbar casing due to such a layout that the DC-DC converter is arranged away from the circuit components. Accordingly, it is difficult to reduce the size of the lighting apparatus.